(1) Field of the Invention
The present invention relates to a method and to a device for treating ice on a windshield of an aircraft, and more particularly of a rotary wing aircraft.
The present invention thus relates to the technical field of de-icing the windshield of an aircraft in the event of flying in icing conditions.
(2) Description of Related Art
Aircraft, and in particular rotorcraft, may operate under flying conditions that lead to windshields icing. By way of example, such rotorcraft may fly at altitudes that are often lower than 10,000 feet or about 3000 meters.
Ice gives rise to operational limitations in aviation. For example, ice degrades the performance of the lift and propulsion members of an aircraft, or indeed its navigation systems.
Furthermore, ice can obscure a windshield and can thus reduce visibility for crew.
In order to combat icing of a member, two methods may be implemented.
A first method is referred to as “anti-icing”. Anti-icing consists in treating a member continuously in order to prevent ice forming on the member under icing conditions.
The anti-icing method presents the advantage of avoiding any deposition of ice. In contrast, the anti-icing method suffers from the drawback of requiring large amounts of energy, given that it operates continuously.
The weight of an anti-icing device and its energy consumption can degrade the potential payload/range, in particular for helicopters where the payload capacity is very sensitive to any change in empty weight.
A second method is referred to as “de-icing”.
It should be observed that the term “de-icing” is sometimes used misleadingly to cover not only de-icing proper, but also anti-icing.
De-icing consists in accepting that ice will become deposited in partial or transient manner, and then in destroying the deposit.
To summarize, anti-icing consists in preventing ice forming, whereas de-icing consists in eliminating ice that has been deposited.
A de-icing system therefore does not operate continuously during flight in icing conditions, but only once a certain quantity of ice has become deposited. Such a de-icing system can then be designed so as to limit its consequences on the empty weight of the aircraft, but at the cost of reduced effectiveness.
The de-icing method thus nevertheless leads to accepting a deposit of ice that might significantly degrade the performance of the aircraft.
In addition, whereas operating an anti-icing system may involve continuously consuming a “moderate” amount of electrical power, operating a de-icing system may involve transient consumption of a large amount of electrical power in order to eliminate a deposit of ice.
Unfortunately, the amount of electrical power available in flight on an aircraft is limited. Under such circumstances, in order to combat ice on windshields, and in particular aircraft windshields, present protection techniques consist essentially in making use of an anti-icing method.
Anti-icing techniques for a windshield may require a heater film or a wire array to be incorporated in the windshield. Sensors, distributed over the windshield, then monitor the surface temperature of the windshield, and switch on or off a stage of heating as a function of reaching temperature thresholds.
Unless countermanded by the crew, the anti-icing system for a windshield is activated continuously during a mission, i.e. before, during, and after the appearance of icing conditions.
Document U.S. Pat. No. 7,928,345 describes a windshield containing within a resistive coating that is connected to an electrical power supply.
Document GB 734 772 suggests using an ammonia-based gas to combat ice.
Document US 2008/0223842 describes a windshield having a resistive coating. The resistive coating is electrically powered at high voltage obtained by transforming low voltage electricity by means of converters and inverters.
That document thus relates to increasing the voltage of an electric circuit powered at 12 volts (V), while an electric circuit of a helicopter anti-icing system conventionally requires powering at 200 V.
Document US 2013/0048622 describes a system for blowing hot air onto a transparent surface.
Also known are Document EP 1 405 742 and Document DE 100 03590.